Dosage-dispensing instruments are generally used for the purpose of dispensing exactly measured small quantities of critical, for example toxic, substances into a target vessel. In many cases the target vessel is placed on a balance, whereby the weight of the dispensed substance can be monitored during the dispensing process and the further discharge of substance into the target vessel can be stopped as soon as a specified target weight has been reached.
Instruments of the current state of the art such as for example the dosage-dispensing device described in commonly-owned EP 1930702 A1 (also available as U.S. Pat. No. 8,245,883) are designed as stationary devices which, in their operating state, are set up on a work surface. These stationary dosage-dispensing devices are characterized in general by a two-part design structure with a dispensing unit and a control unit. The dispensing unit, which contains a supply of the substance to be measured out, includes in particular a dispensing head with a discharge orifice and with means for opening and closing the discharge orifice as well as, in certain cases, for propelling and loosening the powderous or pasteous dosage material. As a further component of the dispensing unit, a source container can be connected to the dispensing head as a way of enlarging the supply volume. The control unit in the dosage-dispensing device of EP 1930702 A1 is a stationary base- or console unit which is designed so that a dispensing unit can easily be set in place as well as removed and exchanged for another dispensing unit.
In the operating state, the discharge orifice of the installed dispensing unit is directed downward, and the means for opening and closing the discharge orifice as well as, in certain cases, for propelling and loosening the powderous or pasteous dosage material are in releasable engagement with propulsion- or actuation elements that are part of the control unit. The dispensing unit in its installed state in the control unit is arranged in a laterally projecting part of the control unit, so as to provide space for a balance below the dispensing unit. For further details, the reader is referred to the European patent application EP 1930702 A1, whose disclosure content in its entirety is hereby incorporated by reference in the present description.
In the dosage-dispensing device described in EP 1930702 A1, the functions of advancing and loosening the powderous or pasteous dosage material are performed through the stirring action of a stirring mechanism in the dispensing head and, in certain cases, a second stirring mechanism in the source container. A further dosage-dispensing device, which is described in commonly-owned EP 1959244 B1 (also available as U.S. Pat. No. 8,191,587), shows the same design structure with a control unit on which an exchangeable dispensing unit is installed. However, the functions of propelling and loosening the dosage material are in this case achieved by imparting shocks to the dispensing unit. The control unit is equipped for this purpose with an impact mechanism, i.e. in essence a hammer mechanism. This solution proves to be particularly advantageous for certain powderous dosage materials such as for example corn starch, which would be compacted by stirring instead of being loosened, so that the flow of material through the dispensing head would be blocked and, as a consequence, no material could be discharged from the dispensing head even with the discharge orifice fully opened. For further details of this dosage-dispensing device with an impact mechanism, the reader is referred to the European patent EP 1959244 B2, whose disclosure content in its entirety is hereby incorporated by reference in the present description.
The stationary dosage-dispensing devices of the foregoing description, which are designed for powderous or pasteous dosage material, are best suited for use at a dosage-dispensing work station that is permanently or temporarily dedicated to this purpose, where a dosage-dispensing device and a balance are set up together and connected either directly or through a computer, so that they work together in a closed feedback loop. However, if the dosage-dispensing applications are of a variable or sporadic nature or are performed with different balances, a permanently set-up dosage-dispensing work station proves impractical. Consequently, there is a need for a portable dosage-dispensing instrument which the user—in order to perform a dispensing process—can hold with one hand above a target vessel that is sitting on a balance, allowing the user to simultaneously monitor the weight display of the balance and to manually regulate the discharge rate of the dosage material and stop the discharge when the specified target weight has been reached.
The idea of using the aforementioned dosage-dispensing devices of EP 1930702 A1 and EP 1959244 B1 directly as handheld dosage-dispensing instruments has been considered, but they proved to be absolutely unsuitable for this application, particularly from an ergonomics point of view. It is hardly possible to hold these devices securely by hand over a target vessel that is sitting on a balance and to simultaneously monitor the weight display of the balance and manually regulate the discharge of the dosage material.
On the other hand, there are numerous state-of-the-art handheld instruments available for the dispensing of fluids, which are commonly referred to as pipettes or handheld pipettes. Of particular interest in the present context are the so-called piston pipettes, among which the pipettes described in EP 1015110 B1 and EP 0496784 B1 may be named as typical examples. Piston pipettes operate according to the displacement principle, meaning that when a movable piston is pushed down, it displaces the air column ahead of it, and when the piston is retracted, it pulls the air column with it, whereby also the liquid that is to be measured is, respectively, pushed out of, or pulled into, the pipette tip which is seated at the end of the pipette. This pipette tip is a disposable article made of plastic. It is the only part that comes into contact with the liquid.
The manual/electronic hybrid pipette described in US 2010/0199789 A1 is likewise a piston pipette, but it differs from the preceding examples in that electronic means with measurement-, calibration- and compensation functions are incorporated directly in the instrument.
The piston pipettes of the foregoing description are of an essentially rod-shaped configuration, wherein the thumb-operated spring-biased plunger knob of the piston is arranged at one axial end of the rod and the pipette tip is arranged at the other end. In the vertical or slightly inclined working position of the pipette, the user's hand grasps the upper part of the rod which is ergonomically designed as a grip handle, so that the thumb rests on the plunger knob.
Obviously, these piston pipettes which serve to dispense liquids are totally unsuitable for powderous or pasteous substances, as these kinds of substances cannot be aspirated into or expelled from the pipette tip with the displacement principle that has been explained above. Furthermore, with the functionally dictated arrangement of the grip handle at the far end from the discharge opening, it is difficult to hold the discharge opening securely and accurately over a target vessel which is in most cases relatively small, particularly while monitoring the weight display of a balance at the same time.
A configuration of a piston pipette that deviates from the customary rod-shaped arrangement is shown in U.S. Pat. No. 7,416,704 B2. A base unit in the shape and size of a grip handle likewise carries at its upper end the thumb-operated plunger knob for the actuation of the piston. However instead of extending downwards in the shape of a rod with a discharge opening at the lower end, the bottom of the base unit is configured as a flat supporting stand, while the discharge opening, on which the disposable pipette tip is placed, is located at the end of a spout which projects at a downward angle from the side of the base unit. The arrangement of the discharge opening on a lateral spout has the advantage that the discharge opening can be held securely and accurately over a target vessel during the dispensing process. However, as in the preceding examples the use of this pipette is limited to the dispensing of liquids.
A handheld dosage-dispensing instrument that is referred to as a “powder pipette” is presented in WO 95/18365. Although this device does not operate according to the piston principle, it has a rod-shaped configuration like the three first examples, wherein one end of the rod is designed as a grip handle with a thumb-operated actuator knob at the end, while the opposite end of the rod contains the discharge opening. The handheld dosage-dispensing instrument is supplied with powder through a lateral opening while the discharge opening is in its closed state. By pushing down on the thumb-operated actuator knob, the shutter mechanism which is designed as a spreader element is opened and simultaneously set into rotation, whereby the dosage material is discharged from the dosage-dispensing instrument.
This dosage-dispensing instrument likewise has the aforementioned disadvantage of a rod-shaped arrangement. A further drawback lies in the fact that the powderous substance that is to be dispensed is obtained from an open container, whereby the outside of the instrument could be contaminated with dosage material. If different substances need to be dispensed, it is almost impossible to reliably clean the interior of the instrument, which presents a problem particularly with substances that are toxic or otherwise critical.
The foregoing examples lead to the conclusion that the aforementioned need for a handheld dosage-dispensing instrument for powderous or pasteous substances is not met by the available state of the art. It is therefore the object of the present invention to create a handheld dosage-dispensing instrument for powderous or pasteous substances which has the capability to perform all of the functions of the above-described stationary dosage-dispensing devices according to EP 1930702 A1 and EP 1959244 B1, with a basic design structure analogous to the dosage-dispensing devices named in these references, i.e. having a control unit and a dispensing unit which can be interchangeably installed in the control unit, but which is distinguished from these stationary devices by a compact, portable design configuration.